API Gateway

An API Gateway sits between clients (Mobile, Web) and services. It acts as a reverse proxy, accepting all API calls, aggregating the various services required to fulfill them, and returning the appropriate result.

When to Use

• Microservices: Essential to hide the complexity of backend services (Service Discovery).
• Cross-Cutting Concerns: Centralizing Authentication, SSL Termination, Rate Limiting, and Logging.
• Protocol Translation: Converting HTTP (Client) to gRPC (Internal).

Core Functionality

Routing

GET /users -> User Service GET /orders -> Order Service

Aggregation (BFF – Backend for Frontend)

Combining results. One request to Gateway -> Calls User Service + Order Service -> Returns combined JSON.

Offloading

• Auth: Validating JWT tokens at the edge.
• Cache: Serving static or cached responses.

Common Patterns

Backend for Frontend (BFF)

Creating specific gateways for different clients (e.g., one for Mobile with small payloads, one for Web with rich payloads).

Best Practices

Do:

• Use mature tools: Kong, Traefik, AWS API Gateway, Nginx.
• Implement Rate Limiting to prevent DoS.
• Use Correlation IDs for tracing requests across services.

Don’t:

• Don’t put business logic in the Gateway (It’s not a service).
• Don’t let it become a Single Point of Failure (High Availability is key).

Troubleshooting

References

• Microservices.io – API Gateway
• Kong Gateway